Unless you live in the deep south of The Netherlands (Zuid-Limburg). iPhone is linked exclusively to T-mobile in The Netherlands and T-mobile has the worst network in terms of coverage of the three providers that operate their own network (KPN, Vodafone, T-mobile). If the iPhone would have been on Vodafone or KPN (both excellent networks), I would have bought one a long time ago. As it is, being on T-mobile is a show stopper.

Exactly. Another option would be some sort of nonconductive coating on the outside of the stainless steel rim/antennae. Must be pretty good, though, as it would wear (but could be easily reapplied too).
There is still that other (rather unlikely) option, namely that iOS4 overcompensates for an increase in signal strength if you short the antennae (and thus increase its size). Doesn't fit with less bars, though. But some interplay with antenna and energy efficiency is still...

Yes, but for instance here in The Netherlands we are stuck with T-Mobile which over here has the worst coverage of all (KPN and Vodafone are best). Were it not for T-mobile coverage (which is so bad they were recently forced to pay compensation to customers), I would have bought an iPhone already.

Is the server software somehow tied to the mini hardware? Or could I buy the new mini, put OS X server on my old mini (which currently runs OS X Server 10.5) and use the new mini as a more powerful desktop?

Ehmmm. If you take away software (not just the OS, don't forget iLife & friends) and design, what is left to compare. A raw list of specifications (limited, e.g. not MTBF stuff) of components? What use is that?
Apple sells 'user experience' more than anything else. More than 'image' (they sell that too, but so is Coca Cola for 99% of their product offering). People are willing to pay for user experience. Many more just look at price and specs and get shafted on user...